What roles knowledge bases play now and will play in the future?
First of all, I would like to point out the main differences between knowledge base and (Deep) machine learning, specially when the main focus is on "AI" not "Data Science":


NNs are like a black box; Even if they learn a dataset and gain the power of generalization over the problem domain, you'd never know how they are working. if you scrutinize the details of the developed model, all you see are digits, weights, poor and strong connections and transform functions. the "feature extraction" step before the training phase literally tells you: "hey human, enough with your complicated world, let's start zeros and ones". In the case of DL, it is worse! we do not even see what the selected and effective features are. I'm not a DL expert but as much as I know, DL's black box is darker! But knowledge bases are written in a human-friendly language. after a knowledge accumulation phase, you could see all the connections between the entities, and more important, you could interpret those connections. if you cut a wire in a knowledge base, your model will lose just a bit of its power, and you know what exactly it will lose; for example disconnecting the "Pluto" node from the "solar system" node, will tell your model what deGrasse Tyson told us. but in a ML model, this might turn it into a pure useless one: what happens if you manipulate the connection between the neuron number 14 and 47 in a NN model used to predict which planets belong to the solar system?!
ML models are merely an inscription of the data. They do not have the power of inference, and they don't give you one. knowledge base is on the other hand capable of inference from the prior knowledge as you indicated in your question. It is shown that DL models that have been trained with say image classification data, could also be applied to voice detection problem. But this doesn't mean DL models could apply its prior knowledge in the domain of images to the domain of voices.
You need kilos of data for traditional ML algorithms and tons of data for DL ones. but a single instance of a dataset will create a meaningful knowledge base for you.


There are two main research topics in NLP: machine translation and question answering. Practically it has been shown that DL works significantly with machine translation problems but acts kind of stupid in question answering challenge, specially when the domain of topics covered in the human-machine conversation is broad. Knowledge bases are no good choice for machine translation but are probably the key to a noble question answering machine. Since what matters in machine translation is only the translated version of a text (and I don't care how on earth has the machine done that as far as it is true) but in question answering problem, I don't need a parrot who repeats the same information I gave it to him, but an intelligent creature who gives me "apple is eatable" after I tell him "apple is a fruit" and "all fruits are eatable". ML models are used to elicit underneath patterns from the dataset (translation) while knowledge bases are used to extend the domain of knowns. ML models nitpick, KBs explore!